How to Reverse a Vector in C++: Simple Guide

To reverse a std::vector in C++, use the std::reverse function from the <algorithm> header. Call it with iterators to the vector's beginning and end like std::reverse(vec.begin(), vec.end()) to reverse the elements in place.

Syntax

The std::reverse function reverses the order of elements in a range defined by two iterators.

• vec.begin(): Iterator to the first element of the vector.
• vec.end(): Iterator just past the last element of the vector.
• std::reverse: Function that swaps elements from start to end until the entire range is reversed.

cpp

std::reverse(vec.begin(), vec.end());

Example

This example shows how to reverse a vector of integers and print the result.

cpp

#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> vec = {1, 2, 3, 4, 5};
    std::reverse(vec.begin(), vec.end());
    for (int num : vec) {
        std::cout << num << ' ';
    }
    std::cout << '\n';
    return 0;
}

Output

5 4 3 2 1 

Common Pitfalls

One common mistake is forgetting to include the <algorithm> header, which causes a compilation error. Another is reversing only part of the vector by using incorrect iterators, which results in only a section being reversed.

Also, trying to reverse a vector by copying elements manually is less efficient and more error-prone than using std::reverse.

cpp

#include <iostream>
#include <vector>
// Missing #include <algorithm> causes error

int main() {
    std::vector<int> vec = {1, 2, 3, 4, 5};
    // std::reverse(vec.begin(), vec.end()); // Error if <algorithm> not included
    return 0;
}

// Correct way:
#include <algorithm> // Must include this
// std::reverse(vec.begin(), vec.end());

Quick Reference

• Include <algorithm> to use std::reverse.
• Use vec.begin() and vec.end() to reverse the whole vector.
• std::reverse modifies the vector in place.
• Works with any container supporting random-access iterators.

Key Takeaways

Use std::reverse with vec.begin() and vec.end() to reverse a vector in place.

Always include header to access std::reverse.

std::reverse works efficiently and avoids manual element swapping.

Be careful to use correct iterators to reverse the intended range.

Reversing modifies the original vector; no new vector is created.